The present invention relates generally to digital communication systems, and more specifically to a destuffing circuit for a TDM (time division multiplex) signal.
As shown in FIG. 1, a prior art destuffing circuit comprises N identical units associated respectively with data signals demultiplexed from an incoming TDM (time division multiplex) signal. In each unit, the data signal is a sequence of frames each containing a pointer representing the start timing of the frame and the type of stuff either positive, negative or zero stuffing. The pointer is detected by a pointer detector 30-i (where i=1, 2, . . . N) and supplied to a stuff discriminator 31-i in which it is examined to see if the frame of the pointer is to be positively or negatively stuffed or zero-stuffed. The output of stuff discriminator 31-i is applied to a selector 32-i for selectively passing one of high-, medium- and low-rate clock pulses from a clock generator 36 to a phase counter 33-i in which the selected clock is counted to produce a binary output. This binary output is applied to a comparator 34-i in which it is compared with the pointer detected by the associated detector 30-i to detect a coincidence therebetween. When this occurs, comparator 34-i produces a signal indicating the start timing of a frame. A timing circuit 35-i is connected to comparator 34-i to generate various timing signals necessary for processing the data signal by using the start-of-frame signal.
However, it is disadvantageous to provide as many phase counters as there are data signals demultiplexed from a single incoming TDM signal as they add to the complexity and overall dimensions of the destuffing circuit.